[SOLVED] DRC error for design from encounter

[parsatt]

Hi All,
I plan to do a fabrication in a digital design technology for the first time( I have only experience in analog before).
When I am done with my design in encounter and attempt to import my design in virtuoso to do the claibre DRC check, I get so many errors on the NW and BP spacing.


Well...Apparently during the cell placement, encounter does not take care of the distances between NWELL or diffusion and this is due to the fact that lef file for the standard cell does not contain any information on the layers beneath the M1!!!

So what I did I just added very long NWELL and BP layers on top of the cell and problem solved!!!!

So I wonder how people with the top level in encounter really fix this problem as calibre DRC is mandatory for sign off!!!!
I really appreciate your comments as I really excited for fix the problem for my very first digital design fabrication.

 

[jbeniston]

Did you add filler cells?

 

[parsatt]

Thanks for the tip,
The thing is that I have all my cells in the design custom designed. (the filler as well).
The thing is that even after placing the fillers I get empty spaces as picture!

I have cells in my lef file as
CELL1 SIZE 0.818 BY 1.592 :
CELL2 SIZE 0.818 BY 1.592
CELL3 SIZE 6.232 BY 1.592

I designed my filler size to be:
FILLER1 SIZE 2.708 BY 1.592 ;
FILLER2 SIZE 1.354 BY 1.592 ;

I think I have followed the rule to cover the digitize size between the cells [6.232-0.818]/2(4). But still I get some empty spaces between.
Again I appreciate your helpful comments.

 

[jbeniston]

Looks like you need to make narrower fill cells, so they can fit in the smallest gap

 

[parsatt]

Yes. I do agree. The thing is that the spaces between the unit cell after the encounter placement is not a digital value and it seems to feel that space you need infinite number of fillers!
Look at the example after the standard cell placement.


In this window at least you need three different filler of width 0.079 0.164 0.083! which in the whole design I need so much more. However from the other pdk library I see the fillers are usually limited to smaller number(i.e 10).
Am I doing something wrong in the cell placement?
or have i made incorrect cells do you think?

 

[jbeniston]

In the LEF file you are using, what do you have for the SITE SIZE definition? You could possibly restrict placement with that.

If not, just create a filler of 0.010 and 0.001. It's not unusually for fillers to be quite narrower than the std cells.

 

[parsatt]

I have only three cells and these are the size Sites for them in lef file:
CELL1 SIZE 0.818 BY 1.592 :
CELL2 SIZE 0.818 BY 1.592
CELL3 SIZE 6.232 BY 1.592

should I use any optimization command in placement in encounter to take care of optimizing these spaces for later on filling?

 

[jbeniston]

What is the SIZE in the SITE definition (not the SIZE of the CELLs - this is usually at the top of the LEF). The SITE definition controls, I think, where the cells can be placed, so you can restrict them to a coarser grid, meaning you'd need less filler cells.

 

[parsatt]

Thank you so much for the advice. As you hinted by adding site definition to the lef file
SITE core_site
SYMMETRY Y ;
CLASS CORE ;
SIZE 0.409 BY 1.592 ;
END core_site
and making all the cells based on this unit size the problem is solved and the filler cells all cover the area and the DRC errors are gone now.

Thanks again.